I not only knew that, it’s what I’ve claimed throughout this thread. You’re agreeing with me now. Light does not appear to travel at the same speed, c, to all observers, unless it’s measured locally. The resolution to the paradox is: You at the top of the building measure the speed of light along the ground at 0.5c, in concordance with the slower clock there. When you see A throw the switch, two microseconds will have elapsed on your clock when you see B’s watch stop. B’s watch will show one microsecond elapsed as B expects.